Nerve electrode

ABSTRACT

A nerve monitoring system facilitates monitoring an integrity of a nerve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. application Ser. No. ______, filedon even date herewith, and entitled “Method and System for Monitoring aNerve”; the entire teachings of which are incorporated herein byreference.

BACKGROUND

The present disclosure relates to nerve stimulation and recordingsystems. In particular, it relates to electrodes adapted to stimulatenerves or record neurogenic responses.

In many invasive medical procedures, steps are taken to preserve healthysurrounding tissues while performing the procedure on a target tissue.In one example, in surgeries involving the head and neck, a surgeon mustguard against unintentional damage to surrounding nerves while excisingother tissue, such as a tumor. This damage may result from direct trauma(e.g. an incision) or “blind” trauma, such as stretching, torsion,compression, ischemia, thermal damage, electrical damage, or othersurgical manipulations. Blind damage is of particular concern becausethe damage may be cumulative over the course of the surgery but may notbe recognizable by the surgeon during the surgery.

One conventional technique of preserving the nerve includes the surgeonperiodically applying a stimulation probe at the nerve andsimultaneously measuring the neurogenic response from an associatedinnervated muscle via electromyography or other techniques. Accordingly,each time the surgeon desires to check the health or integrity of thenerve, the surgeon will maneuver the probe to contact the nerve, andapply the stimulation signal. After measuring and observing the responseto the stimulus, the surgeon removes the probe from contact with thenerve.

Unfortunately, this conventional technique can lead to manyinconsistencies. For example, it is difficult to establish accurateinformation about the response of an unimpaired nerve because thestimulation probe is placed in a slightly different location each timeit is applied, resulting in a slightly different stimulus to the nerve.This contact variability in applying the stimulus leads to a slightlydifferent response pattern. Accordingly, the slightly differentlocations of stimulation tend to cloud ascertainment of a normal ortypical response of the innervated muscle (when the nerve is notimpaired) and also cloud identification of a response signal thatcorresponds to an impairment or disturbance of the nerve. Moreover,because the stimulation probe is applied intermittently, there is noassurance whether the response signal is being measured at the time thatthe nerve is being impaired or being measured at the time the nerve isnot being impaired.

Accordingly, the conventional techniques used during a medical procedureto monitor the health of a nerve fall short of the consistency andaccuracy that would be desirable to reliably ascertain the integrity ofthe nerve during surgery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic illustration of a nerve condition monitoringsystem and including a block diagram of a nerve monitor, in accordancewith principles of the present disclosure;

FIG. 1B is a block diagram of a response module of a nerve monitor, inaccordance with principles of the present disclosure;

FIG. 1C is a block diagram of a baseline module of a nerve monitor, inaccordance with principles of the present disclosure;

FIG. 1D is a block diagram of an impairment sorter of a nerve monitor,in accordance with principles of the present disclosure;

FIGS. 1E and 1F are a series of graphs schematically illustrating amethod of evaluating a neurogenic response of innervated muscle, inaccordance with principles of the present disclosure;

FIG. 2A is perspective view of a nerve electrode, in accordance withprinciples of the present disclosure;

FIG. 2B is a partial sectional view of an electrode contact, inaccordance with principles of the present disclosure;

FIG. 2C is a partial plan view of a contact portion of a nerveelectrode, in accordance with principles of the present disclosure;

FIG. 3 is another perspective view of the nerve electrode of FIG. 2A, inaccordance with principles of the present disclosure;

FIG. 4 is front plan view of the nerve electrode of FIG. 2A, inaccordance with principles of the present disclosure;

FIG. 5 is sectional view of the nerve electrode as taken along lines 5-5of FIG. 3, in accordance with principles of the present disclosure;

FIG. 6 is a side plan view of the nerve electrode, in accordance withthe principles of the present disclosure;

FIG. 7 is a schematic illustration of a method of deploying the nerveelectrode, in accordance with principles of the present disclosure;

FIG. 8 is a flow diagram of a method of monitoring a nerve, inaccordance with principles of the present disclosure;

FIG. 9 is a perspective view of a nerve electrode, in accordance withprinciples of the present disclosure;

FIG. 10 is a side plan view of a nerve electrode, in accordance withprinciples of the present disclosure;

FIG. 11 is partial sectional view of the nerve electrode of FIGS. 9-10,in accordance with principles of the present disclosure;

FIG. 12 is a perspective view of a nerve electrode, in accordance withprinciples of the present disclosure;

FIG. 13 is a sectional view as taken along lines 13-13 of FIG. 12, inaccordance with principles of the present disclosure; and

FIG. 14 is a schematic illustration of a nerve electrode releasablyengaging nerve within a sheath, in accordance with principles of thepresent disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed to electricallymonitoring a nerve during a surgical procedure on a target tissue thatis in the vicinity of the nerve. In general terms, the method includesremovably securing a cuff electrode about the nerve adjacent to thetarget tissue and then establishing a baseline neurogenic response byapplying a series of stimulation signals to the nerve via the cuffelectrode. In some embodiments, the neurogenic response is recorded(e.g., measured) at the innervated muscle via electromyography, while inother embodiments, the neurogenic response is recorded at the nerve as adirect nerve potential. In yet other embodiments, other knownneuro-monitoring techniques are employed to measure and record theresult of neurogenic stimulation or to measure and record a response ona body tissue. For example, in one non-limiting example, the neurogenicresponse is measured and recorded via chemical-based biometrics, such astracking levels of gastric acid, perspiration, or chlorides that areindicate of whether or not a nerve is impaired. In another non-limitingexample, the potential impairment of a nerve is monitored by measuringand recording the neurogenic response via other biometrics, such asmonitoring rhythmic contraction of smooth muscles to move contentsthrough the digestive tract (commonly referred to as peristalsis).

In one aspect, this baseline response generally corresponds to the stateof the nerve prior to any potential impairment related to the surgicalprocedure. Accordingly, after establishing this baseline responsepattern, the surgical procedure is performed on the target tissue whileautomatically stimulating (via the cuff electrode) the nerve with astimulation signal at periodic intervals. Upon comparing a measuredneurogenic response to a periodic stimulation signal relative to thebaseline neurogenic response pattern, one can determine whether thehealth of the nerve is being impaired.

With this in mind, in some embodiments, the term neurogenic refers to aneural-related response or activity initiated by natural neuralprocesses while in other embodiments, the term neurogenic refers to aneural-related response or activity initiated by an external stimulus,such as, but not limited to an evoked potential stimulus. In yet otherembodiments, the term neurogenic refers to a neural-related response oractivity caused by both a naturally neural process and an externalstimulus. In some embodiments, the term nerve refers to neuro structuresin general or some specific neuro structures, including (but not limitedto) one or more of an entire nerve, a nerve fiber, multiple nervefibers, an axon, spatial grouping of axons, or a functional grouping ofaxons within the nerve.

One non-limiting example of automatically monitoring a nerve during asurgical procedure includes monitoring a vagus nerve during a surgery ofthe head and/or neck. For example, in surgeries affecting the thyroidgland, one embodiment of the present disclosure includes removablysecuring a cuff electrode about a nerve, such as the vagus nerve or itsbranches, like the recurrent laryngeal nerve and superior laryngealnerve. In particular, the cuff electrode is placed around the vagusnerve within the carotid sheath with the cuff electrode located proximalor adjacent (relative to the brain stem) to the distal site of thesurgical procedure (e.g., tumor removal). In addition, in someembodiments, an EMG-based endotracheal tube electrode or another type ofinsertable measurement electrode(s) is removably inserted adjacent thevocal cords and/or other muscles innervated by the nerve to bemonitored. In other embodiments, a monitoring electrode, such as a cuffelectrode, is placed about the nerve at a point spaced apart from thelocation at which the stimulation is applied.

With the cuff electrode securely positioned about the nerve, the monitorautomatically stimulates the nerve at periodic intervals (e.g., fromless than one second to greater than 60 seconds, and in-between) and themonitor tracks the neurogenic response. In one aspect, the surgeon canselect the frequency of intervals at which the nerve is stimulated andadjustment of periodic intervals can be based on the urgency of themonitoring. A control of the periodic interval selection includes a slowstimulation rate (e.g., every 60 seconds or less often), faststimulation rates (e.g., every second or more often), and intermediaterates between the slow rate and the fast rate. In one non-limitingexample, faster stimulation rates are used during surgical periods inwhich there is a greater risk to neurologic structures and slowerstimulation rates are used during surgical periods posing with lessrisk. With this arrangement, stimulation to the nerve is applied no morethan necessary in order to avoid potential fatigue of the nerve ormuscle

In one aspect, possible nerve impairment (e.g., due to stretching ormanipulation) is identified by one measured neurogenic response or aseries of measured neurogenic responses that differ from a baselineneurogenic response pattern. These differences are tracked and thesurgeon is automatically notified via graphical alarm information (e.g.,trending patterns, threshold, etc.) and/or audible alarm informationwhen a limit has been exceeded. In one aspect, the audible alarmcomprises a graduated alarm in which a volume of the alarm is inproportion to a level of deviation of the measured neurogenic responsefrom the baseline neurogenic response pattern. Of course, at any timethe surgeon can choose to visually monitor the graphical informationeven when no alarm has been triggered. In one example, a decrease (ortrend of decreases) in amplitude and/or increase in latency from thebaseline response beyond a predetermined or user-defined limit (orcriteria) may indicate deteriorating vagus nerve quality, and uponproviding automatic notification to the surgeon enable the surgeon totake actions to alleviate the nerve impairment.

In some embodiments, a potential nerve impairment is automaticallyidentified by observing a neurogenic response waveform without referenceto a baseline response pattern. In these embodiments, an overallmorphology pattern, synchrony pattern, amplitude, or latency of theneurogenic response includes recognizable irregularities indicative ofnerve impairment. For example, in the context of a synchrony pattern,such irregularities are observable as a response waveform having manypeaks or humps where one or few peaks or humps are expected. In anothernon-limiting example, other irregularities include several peaks orhumps having substantially different peak values instead ofsubstantially similar peak values or instead of substantially harmoniouspeak values. These disrupted synchrony waveform patterns would beindicative of a disorganized response by the various axons or motorunits of the nerve and therefore indicative of nerve impairment.Accordingly, by recognizing certain signatory patterns indicative ofnerve dysfunction, these embodiments can automatically identify nerveimpairment without reference to a measured baseline response pattern onthe monitored nerve.

It is understood that embodiments of the present disclosure are notlimited to monitoring the vagus nerve but apply to other cranial nerves,spinal nerves, or peripheral nerves. This monitoring can be applied tomotor (Efferent) nerves, sensory (Afferent) nerves, and/or mixed nervefiber situations for the somatic and autonomic nervous systems.Moreover, while the electrode is described above in the context ofevoked potential monitoring of nerves during a surgical procedure, it isunderstood that in some embodiments, the electrodes of the presentdisclosure also are employable with implantable stimulators, to providetherapies associated with stimulating other target nerves, including butnot limited to, the vagus nerve.

In some embodiments, the cuff electrode employed in monitoring the nervecomprises an elongate body and a cuff portion. The cuff electrode isconfigured to be removably secured to the nerve to enable stablepositioning of the cuff electrode during the surgical procedure. In oneembodiment, the cuff portion includes a pair of generally curved fingersthat are slidably engageable in a side-by-side relationship. Inparticular, the fingers are configured to releasably engage each otherin a closed position to define a lumen that automatically self adjuststo the proper size to encircle the nerve. The cuff portion is alsoconfigured with a hinge mechanism at a base of the fingers such thatapplication of a pressing or squeezing force on a tab (relative to theelongate body) adjacent the hinge portion causes the fingers to separateaway from each other with their distal tips spaced apart, resulting inan open position of the cuff portion. When in this open position, cuffportion is readily mounted onto, or readily removed from, the nerve.

In another embodiment, the nerve electrode comprises an elongate bodyand a cuff portion. In one aspect, the cuff portion includes a generallyarcuate nerve contact portion of the elongate body and a singleflexible, resilient arm that extends from the elongate body. In an openposition, the arm is free to be slidably maneuvered underneath a nerveand around the nerve so that the nerve contact portion (of the elongatebody) and a proximal portion of the arm define a lumen encircling thenerve. In a further aspect, a distal portion of the arm is slidablyadvanced into a recess of the electrode body to removably secure theproximal portion of the arm in the closed position relative to the nervecontact portion of the elongate body.

By removably securing a nerve electrode (of one of the embodiments ofthe present disclosure) relative to a target nerve and monitoring theensuing neurogenic response, a surgeon can achieve and maintain ahands-free, automatic continuous (or substantially continuous)monitoring of the health and integrity of a nerve in a reliablyconsistent manner during a surgical procedure.

These embodiments, and other embodiments, are described more fully inassociation with FIGS. 1A-14.

A nerve monitoring system 10 is shown in FIG. 1A, in accordance withprinciples of the present disclosure, and comprises a stimulationelectrode 20, a response electrode 30 and a monitor 12 that includes atleast a stimulation module 40 and a response module 60. In generalterms, the stimulation module 40 of monitor 12 applies a stimulationsignal to nerve 22 via stimulation electrode 20 while response module 60of monitor 12 measures a neurogenic response signal at muscle 32 viameasurement electrode 30 (or at nerve 22 via measuring a direct actionpotential with a second cuff electrode similar to and spaced apart fromelectrode 20). The response is communicated to the surgeon via a userinterface 90 of the monitor 12. Accordingly, by using monitor 12, asurgeon can inferentially determine the relative health and function ofa nerve by stimulating that nerve and measuring a correspondingneurogenic response at muscle 32 or at nerve 20.

With the above general construction of system 10 in mind, nervestimulation monitor 12 is further described. In doing so, it isunderstood that the features and components of the monitor 12 can bearranged in many different forms and groupings, and therefore monitor 12is not strictly limited to the particular arrangement or groupings offunctions illustrated in FIG. 1A. Nevertheless, in the illustratedembodiment, monitor 12 additionally comprises a controller 50, memory52, and the previously mentioned user interface 90.

In one aspect, user interface 90 of monitor 12 comprises a graphicaluser interface or other display that provides electronic controltouchpad features, and as such, monitor 12 provides for the simultaneousdisplay and/or activation of the modules (e.g., stimulation module 40,response module 60, etc.), functions, and features of monitor 12described in association with FIG. 1A. In other embodiments, userinterface 90 includes one or more thumbwheels, buttons, or otherelectromechanical control mechanisms for implementing one or more thefunctions of the nerve monitoring system 10. In some embodiments, system10 includes a remote control 54 that is in wired or wirelesscommunication with monitor 12 and that enables a user to control atleast some of the modules, functions, and/or features controllablenormally via user interface 90 but at a distance spaced apart frommonitor 12.

In some embodiments, user interface 90 includes a notify function 92which enables the user to select a preferred format (e.g., graphical,audible, mixed) by which they will receive information about potentialnerve impairment. In one aspect, the notify function 92 communicatesinformation according to one or more specific parameters tracked via anidentification function 66 that will be described later in more detailin association with response module 60 of FIG. 1A. In some embodiments,via visual function 96, the notify function 92 provides graphicalreports of trends in the parameters of a neurogenic response signal toenable the user (e.g., a surgeon) to identify whether potential nerveimpairment is increasing or decreasing depending upon the particularaction taken during the surgical procedure. In some embodiments, eitherapart from or in combination with visual function 96, user interface 90comprises an audio function 94 configured to provide audible alerts toone or more different reports provided by the monitor 12. Among otherreporting functions, the audio function 94 provides an audible alertwhen response module 60 has identified potential impairment of the nervebeing monitored. In one embodiment, based on the measured neurogenicresponse, the audio function 94 provides a faster rate or higher volumeof audible sounds to indicate increased potential for impairment of thenerve being monitored and a lower rate or lower volume of audible soundsto indicate decreased potential for impairment of the nerve beingmonitored. In this way, notify function 92 of monitor 12 providesdirect, ongoing feedback to the surgeon on whether their current courseof actions are improving or impairing the health of the nerve.

In one aspect, the audio function 94 provides information distinct, andindependent from, a conventional acoustic feedback signal reported viaelectromyography. In other embodiments, this acoustic feedback signal ismade selectively available via audio function 94 in addition to thetypes of automatic audio or graphical notification previously describedabove.

In one embodiment, controller 50 comprises one or more processing unitsand associated memories configured to generate control signals directingthe operation of monitor 12 of system 10. In particular, in response toor based upon commands received via user interface 90 and/orinstructions contained in the memory 52 associated with controller 50,controller 50 generates control signals directing operation ofstimulation module 40 and/or response module 60.

For purposes of this application, in reference to the controller 50 theterm “processing unit” shall mean a presently developed or futuredeveloped processing unit that executes sequences of instructionscontained in a memory. Execution of the sequences of instructions causesthe processing unit to perform steps such as generating control signals.The instructions may be loaded in a random access memory (RAM) forexecution by the processing unit from a read only memory (ROM), a massstorage device, or some other persistent storage, as represented bymemory 52. In other embodiments, hard wired circuitry may be used inplace of or in combination with software instructions to implement thefunctions described. For example, controller 50 may be embodied as partof one or more application-specific integrated circuits (ASICs). Unlessotherwise specifically noted, the controller is not limited to anyspecific combination of hardware circuitry and software, nor limited toany particular source for the instructions executed by the processingunit.

In one embodiment, monitor 12 includes at least substantially the samefeatures and attributes as the nerve integrity monitor (NIM) describedand illustrated in assignee's U.S. Pat. No. 6,334,068, titledINTRAOPERATIVE NEUROELECTROPHYSIOLOGICAL MONITOR, and which is herebyincorporated by reference in its entirety.

Referring again to FIG. 1A, stimulation module 40 of monitor 12 includesa frequency function 42, an amplitude function 44, a pulse widthfunction 45, and an electrode function 46. In one aspect, the frequencyfunction 42, amplitude function 44, and pulse width function 45 enableuser selection and tracking of the frequency, the amplitude, and thepulse width, respectively, of a stimulation signal. In another aspect,the electrode function 46 enables user selection and tracking ofstimulation of nerve 22 via nerve electrode 20. In one embodiment, nerveelectrode 20 comprises a cuff-type electrode, as schematicallyillustrated in FIG. 1A. More specific embodiments of nerve electrode 20are described and illustrated in more detail in association with FIGS.2-7 and 9-14.

As illustrated in FIG. 1A, response module 60 of monitor 12 includes oneor more of an amplitude function 62, a latency function 64, an otherresponse parameter function 65, an identification function 66, abaseline function 68, an RF input function 69, an EMG function 70, adirect nerve measurement function 71, an electrode function 72, achemical-based biometric function 73, a tissue-based biometrics function74, and an impairment sorter 75.

In one aspect, the EMG function 70 enables user control over measuringthe response of the muscle via electromyography. In another aspect, viadirect function 71, responses are measured at the stimulated nerve as adirect action potential. In cooperation with the EMG function 70, theelectrode function 72 controls measuring response of muscle 32 viameasurement electrode 30. In one embodiment, measurement electrode 30comprises a typical EMG electrode (e.g., an endotracheal tubeelectrode), which is schematically illustrated in FIG. 1A via dashedlines 30. In one aspect, in cooperation with the EMG function 70, theamplitude function 62 and latency function 64 enable tracking of theamplitude and the latency, respectively, of the response signal measuredat muscle 32 via EMG function 70.

In some embodiments, monitor 12 includes RF input function 69, which ingeneral terms, is configured to receive radiofrequency input associatedwith a monopolar or bipolar electrocautery device used in the surgicalprocedure adjacent the monitored nerve. During the surgical procedure,the electrocautery device can indirectly damage adjacent nerves vialocal heating effects. In addition, direct electrocautery will sever anddestroy tissue. Accordingly, variations in the degree of heating of theadjacent nerves can cause various levels of nerve injury as theelectrocautery device contacts its target tissue. Therefore, trackingwhen an electrocautery device is being used is helpful in determiningwhether impairment of the nerve is caused by electrocautery of tissueadjacent the monitored nerve. If the electrocautery device is determinedto be the likely cause of the impairment, then the surgeon can modifytheir procedure to avoid further impairment to the nerve.

With this in mind, as the electrocautery device is operated it emitsradiofrequency signals which can be tracked and are indicative of whenand how the electrocautery device is being used. Accordingly, in thisone embodiment, RF input function 69 receives RF signals associated withactivity of the electrocautery device. In some embodiments, the RFsignals are obtained via a muting detector feature of monitor 12 whenmonitor 12 includes one or more features and attributes of a monitorhaving substantially the same features and attributes as the previouslyidentified U.S. Pat. No. 6,334,068. In this example, the muting detectormechanism is inductively clamped to an electrocautery probe andtherefore the muting detector mechanism captures an RF signalrepresenting the activity of the electrocautery device. In this way, theRF signal associated with the activity of the electrocautery device isprovided to RF input function 69 to monitor 12.

With the availability of the RF signal via RF input function 69, monitor12 substantially continuously checks to see if a detected impairment tothe monitored nerve is occurring synchronously with (i.e., at the sametime as) heightened activity of the electrocautery device when theelectrocautery device is near the nerve. Accordingly, at the same timethat RF input function 69 is tracking the electrocautery activity, othermechanisms described herein for measuring a neurogenic response (to anevoked potential or stimulation signal) are used to detect whether animpairment is occurring. For example, in some embodiments, theimpairment is detected by measuring a neurogenic response at aninnervated muscle via electromyography, at the nerve as a direct nervepotential, via chemical-based biometrics, or via smooth musclemonitoring, as further described herein in association with FIG. 1A.

Consequently, using both the RF input function 69 and detectedimpairments, monitor 12 determines whether or not a given impairment islikely being caused by an electrocautery device.

In some embodiments, instead of capturing RF signals via the mutingdetector, the RF signals are obtained via other patient leads connectedto monitor 12 that are suitable for picking up RF signals and generallytracking activity of the electrocautery device.

A further description of identifying nerve impairment caused byelectrocautery activity is described later in more detail in associationwith verbal function 98 of FIG. 1A and in association with assessmentmodule 110 of FIG. 1D.

However, prior to measuring a neurogenic response of the target nerveduring a surgical procedure, a user employs the baseline function 68 ofthe response module 60 to determine a baseline neurogenic responsepattern via measurements taken at the innervated muscle 32 or at thenerve 22 upon stimulating nerve 22. In other words, before attempting todetermine whether the integrity of the target nerve is being impaired,the baseline function 68 is employed to determine the response signal orpattern (via amplitude function 62, latency function 64, or otherparameters further described later in association with other responsefunction 65) that normally occurs in the absence of a potential nerveimpingement during a surgical procedure.

In some embodiments, the response module 60 employs identificationfunction 66 of the response module 60 and notify function 92 of userinterface 90 to enable the monitor 12 to automatically notify the userwhen a parameter (e.g., amplitude) of the measured response signaldiffers from a predetermined limit, such as preset percentage of thebaseline response signal (e.g., 25%, 50%, 75%) or some other userdefined setting, criteria, or value.

For example, in some embodiments, the identification function 66 tracksand identifies changes in parameters of the measured response signalrelative to the baseline response pattern. These changes in parameterstracked via the identification function 66 include, but are not limitedto one or more of: (1) one or more decreases in amplitude; (2) one ormore increases in latency; or (3) a decrease in an amplitude-basedenergy (i.e., the area of) of the measured response curve.

In further reference to FIG. 1, in some embodiments, response module 60also includes the chemical-based biometrics function 73 configured tomeasure a neurogenic response (in response to stimulation of a targetnerve) via chemical-based biometrics, such as tracking levels of gastricacid, perspiration, or chlorides that are indicate of whether or not aparticular nerve is impaired. In some embodiments, response module 60also includes the tissue-based or smooth muscle-based biometricsfunction 74 configured to measure a neurogenic response (in response tostimulation of a target nerve) via tissue-based biometrics (or smoothmuscle based biometrics), such as monitoring rhythmic contraction ofsmooth muscles to move contents through the digestive tract (commonlyreferred to as peristalsis).

In further reference to FIG. 1, in some embodiments, the identificationfunction 66 tracks and identifies changes in parameters of the measuredresponse signal (relative to the baseline response pattern) according tothe other response parameter function 65, separately from or incombination with amplitude function 62, latency function 64, and/or anenergy parameter (as part of the amplitude function 62). For example, asschematically illustrated in FIG. 1B, these changes in parameterstracked via the identification function 66 include, but are not limitedto one or more of: (1) a nerve refractory recovery parameter 77configured to identify one or more changes in a nerve recoveryrefractory waveform (as explained in more detail below); (2) a nerveconduction velocity parameter 76 configured to identify one or morechanges in a nerve conduction velocity function; (3) a nerve stimulationthreshold parameter 78 configured to identify one or more changes in anerve stimulation threshold (e.g., the amount of stimulation at whichthe nerve begins to produce an observable neurogenic response); or (4) anerve stimulation saturation parameter 79 configured to identify one ormore changes in a nerve stimulation saturation threshold (e.g., thepoint at which the nerve response signal does not further increase withfurther increased levels of stimulation).

In some embodiments, the nerve refractory recovery parameter 77identifies a potential nerve impairment by monitoring a response of thenerve to a paired stimuli (also know as a paired difference stimulus ora t-test stimulus) which applies a pair of identical stimulus signals toan axon (or a group of axons defining a nerve) separated by a fixed timedelay. In one aspect, this monitoring method is used to provideincreased sensitivity in measuring neurogenic response propertiesbecause of neuronal injury.

In some embodiments, monitoring a neurogenic response to such pairedstimuli protocols includes observing or measuring changes in at leastone of an overall response waveform morphology 77A, a synchrony waveformpattern 77B, an double response time 77C (e.g., the time betweenconsecutive responses), an amplitude 77D, or a latency 77E of theresponse to the second stimulus by itself and/or relative to theresponse to the first stimulus. In some embodiments, this methodincludes applying a series of paired stimuli in which the initial timedelay (between the first stimulus pulse and the second stimulus pulse)is equal to or greater than the natural refractory recovery period (thetime taken for the nerve to fully recovery before a second stimulus isapplied). Thereafter, the monitoring of the nerve is performedcontinually as the time delay between the consecutive first and secondstimuli is gradually decreased (in each successive application of thepair stimuli) to be less than the natural refractory recovery period. Bydriving the time delay to lower and lower values, the monitor 12 candetermine the health of the nerve based on how the nerve responds to thedecreasing time delay between consecutive pulses.

In one aspect, in the context of applying a paired stimuli, the overallresponse waveform morphology 77A illustrates and identifies the extentto which some form of nerve impairment has occurred or is occurringbased on one or more portions (e.g., response pulse width, responsepulse peak, rate of increase to pulse peak, multiple peaks, absence ofsignificant peak, etc.) of the waveform morphology substantiallydiffering from a known response waveform pattern for that type of nerve.Upon recognizing this altered or abnormal morphology, the refractoryrecovery parameter 77 indicates the likelihood of nerve impairment.

In another aspect, in the context of applying a paired stimuli, thesynchrony waveform pattern 77B illustrates and identifies the extent towhich the axons or motor units of a nerve respond together in anorganized manner or synergistic fashion. In other words, in the absenceof nerve impairment, the waveform of the neurogenic response will have arecognizable pattern that corresponds to normal nerve function, as wouldbe recognized by those skilled in the art. However, when the nerve isimpaired, the axons of the nerve will respond in a disorganized manner(e.g., a dissynchronous manner), producing substantial irregularitiesindicative of the various axons responding separately from each other,with some axons not responding at all, some axons responding with aweaker response signal, some axons responding at the wrong time, etc.Accordingly, the synchrony waveform pattern 77B is configured toindicate nerve impairment via automatically recognizing at least aportion of a neurogenic response pattern that includes multipleperturbations or erratic characteristics (e.g., many smaller humpsinstead of a single integrated hump) where a generally smooth orpredictable waveform would otherwise be expected.

In some embodiments, operation of the nerve refractory recovery function77 includes monitoring changes in the refractory recovery period on asegmented basis. In other words, consecutive segments within a singleneurogenic response waveform are compared with each other to observechanges in waveform morphology, synchrony waveform patterns, amplitude,or latency from segment-to-segment that would be indicative of nerveimpairment.

In some embodiments, the nerve refractory recovery parameter 77 isconfigured to perform a comparison of the neurogenic response to thefirst stimulus relative to the neurogenic response to the secondstimulus of the paired stimuli (having a fixed time delay between theconsecutive stimulation pulses), as represented by paired differenceparameter 77F. In this comparison, an algebraic subtraction is performedin which the second response waveform (i.e., the response to the secondstimulus) is inverted relative to the first response waveform (i.e., theresponse to the first stimulus) and then a subtraction is performed ofcorresponding data points of the second response waveform from the firstresponse waveform. When little or no difference is observed based onthis algebraic subtraction, then there is little or no likelihood ofpotential nerve impairment. However, if the comparison via the algebraicsubtraction results in a one or more large observed differences or inmany smaller observable substantial differences, then there is alikelihood of potential nerve impairment. Accordingly, this comparisonprovides a derived response pattern and may be referred to as apaired-difference-response (PDR).

In one aspect, changes in neuronal response observed according tooperation of the nerve refractory recovery parameter 77 as describedabove provide feedback information to the surgeon to indicate that oneor more types of nerve impairment is occurring. These types ofimpairment include, but are not limited to, compression, traction (i.e.,tension), heat injury, or a composite impairment. In one aspect, thetype or degree of impairment is recognized via the observed changes inthe morphology waveform, synchrony waveform pattern, amplitude, latency,or elapsed time (as described above), wherein the observed changes areassociated the various sub-populations of axons arranged concentricallywithin a diameter of the nerve and/or the degree of myelinization of theaxonal elements.

In one aspect, these other response parameters 76-79 associated withfunction 65 provide the capability to detect more subtle changes in aneurogenic response (that might not otherwise be recognized via trackingmore conventional response parameters), which in turn, may detect thedevelopment for potential nerve impairment long before it becomesreadily apparent via conventional monitoring of nerve integrity during asurgical procedure. For example, in another aspect, these other responseparameters (according to other response parameter function 65) providemore discriminating information that would otherwise be available viaconventional acoustic feedback from an innervated muscle, and therebyenable quicker and more effective detection of potential nerveimpairment. In some embodiments, the baseline response pattern trackedvia baseline function 68 is based on (or derived from) one or more ofthe following screening parameters of neurogenic responses (measured inthe absence of potential impingement) according to an exclusion function80 as schematically illustrated in FIG. 1C. These parameters include,but are not limited to: (1) a variability parameter 81 configured toapply a selective exclusion of some responses of multiple evokedneurogenic responses based on a degree of variability of the multipleresponses; (2) a maximum/minimum parameter 82 configured to apply aselective exclusion of a maximum value and/or a minimum value ofmultiple evoked neurogenic responses; or (3) a non-evoked parameter 83configured to apply a selective exclusion of artifacts, such as anynon-evoked neurogenic responses or other artifacts not indicative of anevoked neurogenic response.

In some embodiments, the baseline response pattern tracked via baselinefunction 68 is based on (or derived from) one or more of the followingscreening parameters of neurogenic responses (measured in the absence ofpotential impingement) according to an inclusion function 84 asschematically illustrated in FIG. 1C. These parameters include, but arenot limited to: (1) a single response parameter 85 configured to enableselective use of a single evoked response or of multiple evokedresponses; (2) a statistical mean parameter 86 configured to use astatistical mean of multiple evoked neurogenic responses; (3) a variancemeasuring parameter 87 configured to use variance measuring (e.g.,standard deviation) of multiple evoked neurogenic responses; (4) a ratechange parameter 88 configured to use a rate of change of a series ofevoked neurogenic responses; or (5) a rolling window parameter 89configured to use a continuous sequence (or rolling window) of evokedneurogenic responses. In one aspect, the rolling window parameter 89monitors a generally constant number of evoked neurogenic responses(e.g., 5, 10, or 15) and continually adds one or more new responses tothe set or window while removing the oldest one or more responses fromthe set or window. In this manner, the most recent set (e.g., 5, 10, or15) of responses are always in the monitoring window. In someembodiments, the monitoring window includes responses in series to helpobserve trends, while in other embodiments, the monitoring windowincludes an average of the responses in the window, which is more akinto a rolling average.

In some embodiments, one or more parameters of the baseline function 68are identified via a Poisson distribution, as further described later inassociation with tools module in FIG. 1D.

In one aspect, these screening parameters of baseline response patternfunction 68 are used to establish a baseline response pattern that ismore indicative of a typical baseline neurogenic response than wouldotherwise be ascertained without the sorting process enabled via one ormore of the identified screening parameters. In other words, thesescreening parameters help to ensure that a legitimate difference of themeasured response signal (relative to a baseline response pattern) isidentified because the screening parameters enable removing componentsfrom the baseline response pattern that are atypical within a sample ofmultiple evoked responses.

Referring again to FIG. 1A and keeping in mind the parameters trackedvia the baseline function 68 and via the identification function 66, inone example, the identification function 66 is used to set an alarmlimit relative to the baseline response pattern. In this arrangement, anamplitude of the measured response signal (during the surgicalprocedure) that is less than the alarm limit would trigger anotification of potential nerve impairment via notify function 92.Likewise, in another example, the identification function 66 is used toset a latency limit relative to the baseline response signal or patternsuch that a latency of the measured response signal (during the surgicalprocedure) that exceeds the latency limit would trigger a notificationof potential nerve impairment via notify function 92. In still otherexamples, similar limits are arranged to trigger the notify function 92based on a limit (e.g., criteria, threshold, value) set according to anyone or more of the previously identified parameters of theidentification function 66.

In one aspect, this notification is communicated to the user via userinterface 90 graphically via visual function 96 and/or audibly via audiofunction 94 of user interface 90, as previously described. In someembodiments, the audio function 94 comprises a tone function 97 and/or averbal function 98. As just one example, audio function 94 of monitor 12enables a surgeon to be notified of potential impingement of a targetnerve without requiring the surgeon to look away from their procedure.This audible notification signal provides an immediate “no-look”feedback to the surgeon, thereby enhancing their concentration on thesurgical procedure instead of being distracted with conventionaltechniques of monitoring a nerve. Moreover, because the electrode 20 issecured about nerve 22, the visual function 96 or the audio function 94of the notify function 96 enable the surgeon to monitor the target nervein a hands-free manner, thereby further enhancing their freedom to carryout the main procedure on the target tissue. In some embodiments, thealarm provided via the tone function 97 (of the audio function 94) isconfigured to emit several different types of tones such that eachdifferent type of tone corresponds to a relative degree of deviation ofthe measured neurogenic response from the baseline neurogenic responsepattern. In other words, different tones represent different amounts ofdeviation from the baseline neurogenic pattern.

In some embodiments, audio function 94 includes verbal function 98 whichis configured to provide a notification in the form of a verbalexpression, such as the known words, to the surgeon to inform them ofthe condition of the nerve, such as “normal”, “impairment”, etc. In someembodiments, this verbal function 98 is configured to audibly identifythe type of impairment that is occurring through the use of words suchas “tension”, “compression”, etc. In some embodiments, the verbalfunction 98 is configured to identify the intensity of impairmentthrough the use of words such as “low”, “moderate”, and “severe”.Operation of the verbal function 98 is later described in more detail incooperation with an impairment sorter 75 that is illustrated anddescribed in association with FIG. 1D.

In further reference to FIG. 1A, in some embodiments, the alarmsprovided via the audio function 94 or the visual function 96 comprise agraduated alarm function 97 in which a volume of the alarm (audible orgraphical) is in proportion to a degree of deviation of the measuredneurogenic response from the baseline neurogenic response pattern.

In some embodiments, the response module 60 includes an impairmentsorter 75, which is further illustrated in FIG. 1D. As shown in FIG. 1D,impairment sorter 75 includes an assessment module 102 and a reportmodule 104.

In general terms, the report module 104 operates in cooperation with thenotify function 92 of user interface 90 and is configured to report thecondition of the monitored nerve to the surgeon. In some embodiments,the report module 104 includes a type function 124 and an intensityfunction 125. In general terms, the type function 124 indicates the typeof damage identified via the differentiator function 112, such aswhether the nerve is experiencing minor irritation, tension,compression, a composite impairment of both tension and compression, orimpairment directly or indirectly caused by electrocautery (aspreviously described in association with RF input function 69 in FIG.1A).

Accordingly, when there is some impairment of the monitored nerve, thenthe type of impairment is communicated via verbal function 98 as one ormore verbal expressions (e.g., words like tension, compression, etc.) inreal-time to the surgeon during surgery.

In general terms, the intensity module 125 of the report module 104 isconfigured to provide an indication (via verbal function 98 of notifyfunction 92 in FIG. 1) to the surgeon of the relative intensity of theimpairment of the nerve. In one embodiment, the intensity module 125includes a low function 126, a moderate function 127, and a severefunction 128. Accordingly, when there is some impairment of themonitored nerve, then any such impairment is communicated via verbalfunction 98 as a verbal expression in real-time to the surgeon duringsurgery. In one aspect, such verbal expressions include, but are notlimited to, the words low, moderate, or severe or other similar meaningwords that indicate a relative degree of intensity. Further, in someembodiments, intensity function 125 provides and communicates at leasttwo different levels of intensity.

In some embodiments, the assessment module 102 of impairment sorter 75includes a tools module 104 and a differentiator module 112. In generalterms, the tools module 110 is configured to apply different forms ofstatistical analysis and/or other filters to sort data of one or moremeasured neurogenic responses. In cooperation with differentiator 112,the tools module 110 removes noise while transforming the data to moreaccurately identify changes in nerve function with such changesincluding changes in amplitude, latency, or other enumerated aspects ofnerve function previously described in association with identificationfunction 66 in FIG. 1. Recognition of these changes fromresponse-to-response or over time through multiple responses provides anindication of the type or extent of impairment to a nerve.

In one embodiment, the tools module 110 includes a distribution function114, a correlation function 116, a wavelet function 117, and a Fourierfunction 118.

In one embodiment, the distribution function 114 is configured torecognize which type of statistical distribution that best characterizesneurogenic responses (for example, EMG responses) resulting fromstimulation pulses. In one example, the neurogenic responses fit bestwithin a Poisson distribution and therefore observations regarding theneurogenic response information is calculated from the Poissondistribution. However, other distributions are not excluded. In a fewnon-limiting examples, by using the Poisson distribution the mean of thereceived data provides a measure of the average delay while a standarddeviation provides a measure the degree to which the responses areerratic. As another example, changes in the delay and signal spreadrecognized in the distribution are indicative of possible nerveimpairment. In another aspect, the Poisson distribution is used todisregard some data as spontaneous activity. For example, thisdistribution can be used to disregard EMG responses appearing at a farend a lower tail of the Poisson distribution or appearing at a far endof an upper tail of the distribution because there is a very lowprobability that such responses are truly indicative of the condition ofthe nerve.

In some embodiments, this distribution tool 114 is used in cooperationwith or as part of baseline function 68 of response module 60, aspreviously described in association with FIG. 1A.

The other functions of tools module 110 generally relates to classifyingdifferent features of the measured neurogenic response signals with suchfunctions including but not limited to a correlation function 116, awavelet function 117, and a Fourier function 118. In general terms, thespreading or narrowing of the EMG response as well as the responseamplitude and overall shape of the EMG response is used to identify adamaged or stressed nerve. Further, these methods of classificationprovided via tools module 110 are used to classify the response waveforminto different categories that identify the type and/or extent of theimpairment. In one aspect, these methods are used to augment the currentmethods or employed as a separate method of classifying aspects of theresponses to indicate the extent or type of nerve impairment.

In some embodiments, the correlation function 116 is configured toprovide auto-correlation and or cross-correlation techniques are used toidentify the EMG response waveform as a recognizable stimulated responseso that other aspects of a response signal not following such patternscan be ignored. In one aspect, the received data of neurogenic responsesis correlated relative to stored response waveforms of different typesto classify the response. In one non-limiting example, a first storedresponse waveform is indicative of compression on a nerve while a secondstored response waveform is indicative of excess tension on the nerve.When a waveform in the received data matches one of these respectivefirst or second stored response waveforms, then the correlation function116 provides an indication of whether the impairment on the nerve iscompression or tension. In some embodiments, the neurogenic responsewaveform is also correlated relative to a baseline response pattern ofthe target nerve to evaluate changes in the response of the nervecompared to the responses occurring prior to surgery.

In some embodiments, the wavelet function 117 provides another mechanismto classify the response data to recognize patterns indicative of a typeor extent of nerve impairment. Likewise in some embodiments, a Fourieranalysis is applied via Fourier function 118 to the response data toidentify the frequency content of the signals to enhance theidentification of changes to the nerve function and/or recognize changesover time. One example of the application of the Fourier function 118 islater described in more detail in association with FIG. 1E and FIG. 1F.

In general terms, the differentiator 112 further sorts the resultsobtained from tools module 110 to place the measured neurogenicresponses into different categories that communicate to the surgeon thetype of ongoing trauma to the monitored nerve. In one embodiment, thedifferentiator 112 includes an irritation parameter 120, a tensionparameter 121, a compression parameter 122, a composite parameter 123,or an electrocautery parameter 129.

In some embodiments, differentiator 112 also assists in identifying ordifferentiating the size of nerve fibers affected by the nerveimpairment. For example, the response latency is used to differentiatesurgical damage according to the size of the nerve fibers.

In particular, the nerve conduction velocity of the stimulated responsepropagation is related to the diameter of the axons of the nerve and tothe presence or absence, or condition of the myelin sheath. For example,increased nerve conduction velocities are associated with the presenceof a myelin sheath and associated with larger nerve axons, resulting ina relatively shorter response latency. In one aspect, damage to themyelin sheath will decrease the conduction velocity, and increase theresponse latency. In another aspect, by tracking the response latency,one can differentiate the surgical damage relative to the size of thenerve fibers. For example, larger axons will move the signal faster, andthereby produce the shortest latency. Another observable featureincludes a larger electromyography response for larger axons whichinnervates neuromuscular junctions and therefore activates a greaternumber of motor nerve units.

With this in mind, the irritation parameter 120 identifies a generalirritation to the monitored nerve caused by minor tension and isdetected by an increase in the response latency and an increase in theevoked response amplitude. The tension parameter 121 identifiesimpairment by excessive tension and is detected by an increase inresponse latency and a decrease in the evoked response amplitude. Inparticular, this excessive tension typically damages the myelin sheaththereby increasing the response latency while the decrease in amplitudeis caused by damage to the large axons of the nerve.

The compression parameter 122 identifies impairment by excesscompression on the nerve and is detected by a decrease in evokedresponse amplitude without a substantial change in latency. Inparticular, this compression is associated with damage to the nervewhich results in activation of a decreased number of motor unitsresulting in the decrease in measured amplitude. Because thiscompression generally does not significantly affect the myelin sheathover a significant distance, there is no major change in latency.

The composite parameter 123 identifies impairment by more than one typeof impairment, such as both compression and tension.

In some embodiments, the electrocautery parameter 129 identifiesimpairment at least partially caused by an electrocautery eventimpacting the nerve and is detected via an occurrence of one of thepreviously described types of nerve impairment simultaneous with orsynchronously an electrocautery event or activity during the surgicalprocedure. For example, electrocautery parameter 129 of differentiatorfunction 112 substantially continuous monitors an RF signal forelectrocautery event waveforms via RF input function 69 of monitor 12,as previously described in association with FIG. 1A. When one of thetypes of impairment (irritation, tension, compression, composite) isseparately identified via the measured neurogenic response signals, theelectrocautery parameter 129 of differentiator 112 checks to see if theidentified impairment occurred synchronously with (at the same time as)an electrocautery event or recognizable electrocautery activity. If so,electrocautery parameter 129 indicates that an electrocautery impairmentlikely has occurred. This information can guide the surgeon to modifytheir surgical procedure to avoid any further impact to the nerve duringuse of the electrocautery device.

Accordingly, in cooperation with the verbal function 98 of notifyfunction 92 (FIG. 1A), differentiator 112 provides a real-time audibleindication as a verbal expression to the surgeon of the type ofimpairment occurring on a monitored nerve, such as an irritation,tension, compression, composite, or electrocautery impairment. Uponhearing such notification, the surgeon can immediately modify or adjusttheir technique to reduce and/or avoid further impairment to bemonitored nerve situated adjacent to their primary surgical target.However, it is understood that other verbal expressions (i.e. wordsother than irritation, tension, compression, composite, orelectrocautery) are selectable or programmable to be audiblycommunicated to represent the underlying respective general irritation,tension impairment, compression impairment, composite impairment, orelectrocautery impairment.

In this way, assessment module 102 and report module 104 of impairmentsorter 75 further enable the hands-free and watch-free monitoring of anerve during surgery.

FIG. 1E provides a series of graphs 130, 132, 134, 136 thatschematically illustrate, in both the time domain and the frequencydomain, an electromyography (EMG) response as a baseline responsepattern and as a response signal after injury of the monitored nerve. Ingeneral terms, by applying a fast Fourier transform to this signalinformation, one can accurately identify the change in the function ofthe nerve due to impairment while excluding data that is not indicativeof this change. With this in mind, graph 130 illustrates a baseline EMGresponse via signal 131A that has a peak amplitude 131B while graph 132illustrates a baseline EMG response after application of a Fouriertransform. As illustrated in graph 132, the transformed signal 133Aincludes a first peak 133B, a second peak 133C, and a third peak 133D.The first peak 133B indicates a response amplitude of about 13 while theother peaks 133C, 133D illustrate significantly lower amplitudes in thefrequency domain.

As illustrated and described above in association with FIG. 1E, theFourier transform is applied in a method of identifying one or moresignal features of the baseline response pattern (such as, but notlimited to, an amplitude) that are indicative of a condition of a nerve.Accordingly, this method includes, at least, comparing the baselineresponse pattern as expressed in the frequency domain relative to thesame baseline response pattern as expressed in the time domain.

In comparison to graph 130, graph 134 illustrates an EMG response afteror during impairment to the nerve. As shown in graph 134, responsesignal 135A includes a peak 135B having an amplitude significantly lowerthan that shown in graph 134 (i.e., the baseline response of themonitored nerve). However to ensure that an accurate observation is maderegarding any changes to condition of the nerve, a Fourier transform isapplied to the signal 135A (in graph 134) which results in the signal137A illustrated in graph 136. By observing the response after or duringimpairment in the frequency domain provided via graph 136, a single peak137B corresponding to the response amplitude is clearly recognizable anddistinguished from other aspects of the response signal. By comparingthe transformed signal 137A in graph 136 and the transformed signal 133Ain graph 132, the Fourier function 118 of tools module 110 identifies asignificant change in the response amplitude after injury. Inparticular, graph 132 illustrates a response amplitude of about 13 priorto injury while graph 136 illustrates response amplitude of about 5after injury. Accordingly, by using the Fourier function 118, a clearindication is provided of the altered condition of the nerve as detectedby a change in the response amplitude to a stimulation pulse.

As illustrated and described above in association with FIG. 1E, theFourier transform is applied to the measured neurogenic response signalin a method of identifying one or more signal features (such as, but notlimited to, an amplitude) indicative of a condition of a nerve.Accordingly, this method includes, at least, comparing a measuredneurogenic response signal as expressed in the frequency domain relativeto the same measured neurogenic response signal as expressed in the timedomain.

FIG. 1F provides a further schematic illustration of application ofFourier function 118 to an EMG response signal. In particular, FIG. 1Fprovides graph 140 which illustrates a measured EMG response signal 141Aafter or during impairment to a nerve where noise is present in thesignal. As shown in graph 140, signal 141A illustrates a first responsepeak 141B and a series of peaks 141C expected to be caused from noise.Meanwhile, graph 142 illustrates a signal 143A that represents themeasured EMG response signal 141A of graph 140 after application of afast Fourier transform via Fourier function 118. As shown in graph 142,the neurogenic response signal is clearly recognizable as peak 143B(based on its similarity to amplitude waveforms of prior neurogenicresponses) whereas the noise when expressed in the frequency domain doesnot match the waveform of a response signal and is excludable from peak143B. In one aspect, dashed lines N-N represent a demarcation of theresponse signal waveform (including peak 143B) from the noise appearingto the right of the dashed line and represented by indicator 144.

As illustrated and described in association with FIG. 1F, the Fouriertransform is applied to the measured neurogenic response signal in amethod of identifying one or more signal features (including, but notlimited to, an amplitude) indicative of a condition of a nerve.Accordingly, this method includes analyzing the measured neurogenicresponse signal in the frequency domain to differentiate noise from thesignal features of the measured neurogenic response signal. In oneaspect, this differentiation is performed by recognizing the noise ashaving a pattern in the measured neurogenic response signal in thefrequency domain that is substantially different than a pattern of thebaseline response pattern in the frequency domain or substantiallydifferent than a pattern of one or more prior measured neurogenicresponse signals (in the frequency domain) without noise.

Accordingly, different classification tools and reporting tools asprovided via impairment sorter 75 provide a useful mechanism to sort andevaluate one or more neurogenic responses, which in turn, enhances theability to detect and classify different types of impairment to a nerve.

FIGS. 2-7 are different views that illustrate a nerve electrode 150, inaccordance with principles of the present disclosure that is usable tostimulate a nerve or record a response at a nerve. As illustrated in theperspective views of FIGS. 2 and 3, electrode 150 comprises an elongatebody 152 and a cuff portion 160. The nerve electrode 150 includes aproximal end 156 and a distal end 157. In one aspect, the elongate body152 includes a distal portion 158 adjacent the cuff portion 204 andextends from the distal portion 158 to the proximal end 156 of theelectrode 150. In some embodiments, elongate body 152 comprises a ribbedsurface 154 and a smooth surface 165 on each of two opposite faces 167of elongate body 152. In another aspect, elongate body 152 includesopposite side edges 169, which are generally smooth in some embodiments.

In further reference to FIGS. 2-4, each respective face 167 has a width(W1 in FIG. 4) substantially greater than an average width (W2 in FIG.6) of each respective side edges 169. In another aspect, elongate body152 has a length (L1) substantially greater than an inner diameter (D1)of cuff portion 160, as illustrated in FIG. 5. In one non-limitingexample, the length L1 is at least twice as large as, and up to tentimes larger than, the inner diameter D1. In another aspect, the width(W1) of face 167 of elongate body 152 (FIG. 5) is substantially greaterthan the width (W2 in FIG. 6) of side edge 169. In one non-limitingexample, the width W1 is at least twice as large as, and up ten timeslarger than, the width W2.

Accordingly, because the elongate body 152 is substantially longer thana diameter of the cuff portion 160 (and of the lumen 185) and has asubstantial width (W1), the elongate body 152 provides a strong supportor anchor against which forceps can be used to move tab 162 toward andagainst the elongate body 152, as further described and illustratedlater in association with FIG. 7. In one aspect, the substantial widthof the elongate body 152 provides an ample target that the distal tipsof the forceps can grasp while the substantial length (L1) of theelongate body provides better reach to facilitate advancing the cuffportion 160 about the nerve 22. With these features in mind, elongatebody 152 is sometimes herein referred to as a beam or trunk.

Referring again to FIGS. 2-4, the cuff portion 160 extends distallydirectly from the distal portion 158 of elongate body 152. In oneembodiment, the cuff portion 160 includes a first finger 172 and secondfinger 174 arranged in a side-by-side relationship (FIGS. 2-5) andextending from a base portion 177. As best seen in FIGS. 5-6, eachfinger 172, 174 defines a generally arcuate cross-sectional shape. Inone aspect, the base portion 177 defines a junction between, andsupports both of, the elongate body 152 and tab 162. As furtherdescribed later, the elongate body 152 and tab 62 also act as a pair ofgroup members of an actuator mechanism while the base portion 177 alsofunctions as a hinge controllable by the actuator mechanism to enablerotational movement of first finger 172 and second finger 174 away fromeach other, as illustrated in FIG. 7. In particular, the base portion177 includes a central bending region or central hinge region(represented via dashed lines 178) approximately midway between thetrunk 152 and tab 12 such that trunk 152 is off-axis relative to thiscentral hinge region 178. Stated differently, the central hinge region178 is laterally offset relative to (i.e., not aligned with) alongitudinal axis (represented by line Z as shown in FIG. 6) of trunk152.

In some embodiments, each finger 172,174 comprises a generally circularcross-sectional shape (best seen in FIGS. 5-6) while in otherembodiments, each finger 172,174 comprises a generally ellipticalcross-sectional shape. When in their at-rest, closed configuration, theside-by-side combination of the generally circular fingers 172, 174define lumen 185 which is sized and shaped to receive a nerve.

Moreover, because the respective fingers 172, 174 are in thisside-by-side relationship along a length of the lumen (i.e., in adirection generally parallel to a longitudinal axis of the nerve thatwill extend through lumen 185), each finger 172, 174 independentlydefines at least a portion of a length of the lumen 185.

Moreover, in one aspect, in combination with base hinge portion 177,each respective finger 172, 174 independently provides a substantially360 degree coverage that encompasses a circumference of the targetnerve. In another aspect, in combination with base hinge portion 177, apair of fingers 172, 174 act together to effectively provide more than360 degrees (and up to 570 degrees) of coverage that encompass thecircumference of the target nerve to the extent that the distal portionof the respective fingers 172, 174 overlap in a side-by-side fashion.

In yet another aspect, the independent 360 degree coverage encompassingthe nerve by the separate fingers 172, 174 also provides an automaticmechanism for the nerve electrode 150 to self-adjust its size todifferent sized nerves while maintaining the electrode contact 180 indirect pressing contact against an outer surface of the nerve. Thisarrangement contributes to the sealing action of the lumen 185 againstan outer surface of the nerve, thereby preventing intrusion of fluids orother matter into the nerve-electrode contact interface, which in turnimproves the reliability and quality of the stimulation or recordingsignal.

In some embodiments, as best seen in FIG. 6, with base portion 177extending at least from trunk 152 to tab 162, first finger 172 has aradial length generally equal to a radial length of second finger 174wherein a tip 214 of second finger 174 is represented by dashed line219. However, it is understood that in other embodiments, the firstfingers 172 has a substantially different length than second finger 174.

As best seen in FIGS. 2-4, first finger 172 includes a generallystraight outer edge 200 and a generally angled inner edge 202, whichconverge to form a curved junction at a distal tip 204. Similarly,second finger 174 includes a generally straight outer edge 210 and agenerally angled inner edge 212, which converge to form a curvedjunction at a distal tip 214. In one aspect, as best seen in FIGS. 3-4,the generally angled inner edge 202 of the first finger 172 forms agenerally helical relationship relative to the generally angled firstedge 212 of the second finger 174. Stated in other terms, the generallyangled inner edge 202 of first finger 172 and the generally angled inneredge 212 of second finger 174 form complementary angles relative to eachother (as represented by the complementary angles θ and σ illustrated inFIG. 4).

In one aspect, this complementary relationship between the inner edge202 of the first finger 172 and the inner edge 212 of the second finger174 enables the first finger 172 and the second finger 174 to be inreleasable, slidable contact against each other in a nested arrangement.In one aspect, this nested arrangement enables the angled, side-by-sidefingers 172, 174 to provide a more robust enclosure about a nerve thanif the inner edges of the fingers were simply generally parallel to eachother (along a line generally perpendicular to the lumen or along a linegenerally parallel to the lumen) or than if the distal ends of thefingers simply contacted each other in a conventional end-to-end closedrelationship. In other words, the angled, nested relationship of thefingers 172, 174 results in releasable interlocking of the fingers 172,174 relative to each other, thereby helping to prevent possibledislodgement of the nerve electrode 150 from becoming dislodged from thenerve about which it is removably secured. Moreover, this releasableinterlocking feature of the fingers 172, 174 insures that the electrodecontact 180 remains in stable and close fitting contact against thenerve, thereby contributing to accuracy and consistency in applying astimulation signal to the nerve via the nerve electrode 150.

In another aspect, each finger 172,174 comprises a semi-flexible,generally resilient member. With this construction, the respectivefingers 172, 174 generally retain their generally circular or generallyarcuate shape in their closed position (shown in FIGS. 2-6) and in theiropen position shown in FIG. 7. On the other hand, as the fingers 172,174 move from their closed position to their open position shown in FIG.7, the base hinge portion 177 (defining a junction between elongate body152 and tab 162) flexes considerably to permit rotation of the tab 162toward and against distal portion 158 of elongate body 152. Accordingly,as shown in FIG. 7, the hinge portion 177 generally straightens out toforce the distal tips of the respective fingers 172, 174 away from eachother. However, as soon as the pressing action of the forceps 194 isremoved, tab 162 automatically rotates back to its at-rest position(best seen in FIGS. 2-3 and 5) due to the resiliency of the base hingeportion 177 of cuff portion 160 and thereby allows the return of thefingers 172, 174 to their closed position. In one embodiment, base hingeportion 177 comprises a generally resilient or elastic living hinge, aswould be understood by one skilled in the art. With this in mind, beam152 and tab 162 act as pair of oppositely disposed grip members of anactuator mechanism such that pressing action of the respective gripmembers activates bending of base hinge portion 177 to causedisplacement of fingers 172, 174 away from each other into the openposition and release of these grip members reverses bending of basehinge portion 177 to cause fingers 172, 174 to once again releasablyengage each other in a side-by-side manner. In some embodiments, infurther reference to FIGS. 2-6, first finger 172 includes asubstantially larger base portion 215 (adjacent tab 162) than a baseportion 205 (FIG. 6) of second finger 174. In one aspect, the large baseportion 215 of first finger 172 extending from tab 162 provides a robustsupport structure to withstand the stress induced when tab 162 isrotated toward elongate body 162 (to move the fingers 172, 174 to theiropen position) as shown in FIG. 7.

In some embodiments, the body of nerve electrode 150 is formed of amolded elastomeric material suitable to provide the elastic performanceof the base hinge portion 177 of electrode 150. In one embodiment,electrode 150 is molded from a rubber material, from a siliconeelastomeric material, or other elastomeric material.

In one aspect, as best seen in the sectional view of FIG. 5, electrodelead 182 extends through elongate body 152 with a distal portion of theelectrode lead 182 including an electrode contact 180 exposed at surface161 of cuff portion 160. It is also understood the nerve electrode 150generally includes lead 182 and that the lead 182 is omitted from FIGS.2-4 and 6-7 merely for illustrative clarity. Referring again to FIG. 5,a proximal portion of lead 182 extends outwardly from the proximal end156 of the body 152 for electrical connection to, and electricalcommunication with, the monitor 12. In one aspect, the electrode contact180 is a generally circular shaped member of electrically conductivematerial and is in general alignment with a longitudinal axis of beam152 and lead 182 extending through beam 152. In one embodiment, the beam152 and a lead 182 extend and a substantially single directionthroughout an entire length of the beam 152.

In some embodiments, the electrode contact 180 includes a generallycircular shape defining a first area and the contact portion 161 of theelectrode 150 surrounding that the electrode contact 180 defines asecond area that is substantially larger than the first area. Incombination with the gripping action of the fingers 172,174 (whichmaintains the electrode contact 180 in pressing contact against an outersurface of the nerve), the substantially larger area of the surroundingcontact portion 161 of cuff portion 160 further seals thenerve-to-electrode interface apart from unwanted fluids or othermaterial that could otherwise interfere with the measurement orstimulation on the nerve through the nerve-to-electrode interface.

However, it is understood that in some other embodiments, electrodecontact 180 is replaced with an array of spaced apart electrode contactarranged on the contact portion 161 of cuff portion 160 and/or of thefingers 172, 174.

In general terms, the electrode contact 180 of the nerve electrode 150is configured to enhance a bioelectric contact interface and therebyenhance stimulation and/or recording of neurogenic responses of thetarget nerve. Accordingly, in some embodiments, the electrode contact180 comprises a contact material or a contact plating material made froma biocompatible metal (or noble metal) that includes (but is not limitedto) one or more of the following materials: 316 Stainless Steel, silver,gold, platinum, palladium, or rubidium. In some embodiments, the contactmaterial or contact plating material of electrode contact 180 is madefrom a conductive filled flexible circuit, elastomeric material, aconductive ink, or vapor deposited conductor. Moreover, in addition toincorporating a particular type of material, in some embodiments theelectrode contact 180 is configured to increase a contact surface areavia an irregular surface 185 (such as an undulating surface, a knurledsurface, a brushed surface, etc.) as illustrated in FIG. 2B.

In other embodiments, electrode contact 180 is configured to decrease acontact resistance via sintering of the electrode contact or via etchingof the contact. As further illustrated in FIG. 2C, drugs are embedded inelectrode contact 180 and/or contact portion 161 of nerve-engaging cuff160 (as represented by markings 186) via mixing or molding the drugswith the respective conductive or elastomeric materials duringconstruction of the electrode contact 180 or contact portion 161. Theembedding of drugs enables them to be defused from nerve electrode 150during surgery or during long term implantation. The embedded drugsinclude, but are not limited to, anti-inflammatory agents or drugs topromote implant integration and biocompatibility.

In some embodiments, barium sulfate is added to and mixed with theelastomeric material so that the molded nerve electrode 150 forms avisibly radio opaque element viewable under radio fluoroscopy.

In some embodiments, nerve electrode 150 includes the tab 162 forming aprotrusion that extends outward from outer portion 168 of cuff portion160. In one aspect, tab 162 includes a wall portion 190 and a lip 192.In one aspect, the lip 192 extends in direction generally opposite tothe elongate body 152 and is configured to reciprocally engage (i.e.,releasably catch) a distal tip of a forceps, as further described laterin association with FIG. 7. In another aspect, as best seen in side planview of FIG. 6, tab 162 forms an angle (as represented by a) that is asub-straight angle (i.e., less than 150 degrees) relative to beam 152.In some embodiments, the angle (α) is between about 30 to about 110degrees relative to the beam 152. However, in some embodiments, theacute angle is at least about 40 and may extend up to about 90 degrees,while in other embodiments the acute angle is between about 60 to about70 degrees. In one embodiment, the acute angle between tab 162 andelongate body 152 is about 67 degrees.

FIG. 7 is a schematic illustration of a method of installing electrode150, in accordance with principles of the present disclosure. In thismethod, a surgeon uses a tool such as a forceps 194 with a squeezingaction so that one distal tip 196A of the forceps 194 presses againstthe tab 162 and engages the lip 192. At the same time, the other distaltip 196B of the forceps 194 presses against the ribbed surface 154 ofthe elongate body 152. In one aspect, distal tip 196B engages between apair of ribs of the ribbed surface 154 to prevent slipping of distal tip196B during the pressing action of the forceps 194. With this pressingaction, the user further manipulates the arms 198 of the forceps 194 tosqueeze the tab 162 toward the elongate body 152, thereby moving thedistal tip 204 of the first finger 172 away from the distal tip 214 ofthe second finger 174. In other words, pressing action of the tab 162toward the elongate body 152, results in the bending of the base hingeportion 177 and the formation of an opening 220 between the distal tip204 of first finger 172 and distal tip 214 of second finger 174.

With the cuff portion 160 in this opened position, the cuff portion 160is maneuvered about the target nerve 20 until both the contact surface161 and the electrode contact 180 of the cuff portion 160 engage thetarget nerve 20, at which time the surgeon releases tab 162 (via openingof distal tips 196 of forceps 194). This action allows the first andsecond fingers 172, 174 to be released from their open position to theirclosed position in which first and second fingers 172, 174 resume theirside-by-side, releasable interlocking relationship (FIGS. 2-6) thatdefines lumen 185 encircling the nerve 20.

Keeping in mind the construction of the nerve electrode 150, FIG. 8illustrates a method 275 of monitoring a nerve during a surgicalprocedure on a target tissue, in accordance with principles of thepresent disclosure. In one embodiment, method 275 is performed using asystem and/or cuff electrode having at least substantially the samefeatures and attributes as the system 10 and cuff electrodes 20, 150, aspreviously described in association with FIGS. 1-7. However, in anotherembodiment, method 275 is performed using systems and/or electrodesother than those described and illustrated in association with FIGS.1-7.

Referring again to FIG. 8, at 280 method 275 comprises removablysecuring a cuff electrode about a nerve adjacent to the target tissueand then establishing a baseline neurogenic response pattern of thenerve by stimulating the nerve via the cuff electrode, as shown at 282,in which this neurogenic response is measured at an innervated muscle ordirectly at the nerve. As shown at 284, the surgical procedure isperformed on the target tissue while automatically stimulating (via thecuff electrode) the nerve with a stimulation signal at periodicintervals. The method 275 also includes measuring neurogenic responsesto each periodic stimulation signal relative to the baseline neurogenicresponse pattern (as shown at 286) and then monitoring differencesbetween the measured neurogenic responses and the baseline neurogenicresponse pattern relative to a limit, as shown at 288. The limit can bea user-defined value, criteria or other threshold. As shown at 290, whenthe limit is exceeded, the surgeon is then automatically notified (viagraphical means or audibly) of any monitored differences or trends ofmonitored differences that may be indicative of potential impairment tothe nerve.

Accordingly, because the cuff electrode is secured about the nerve andthe method automatically applies the stimulation signal at periodicintervals, the surgeon can monitor the nerve in a hands-free mannerwhich allows the surgeon to devote more attention to the surgicalprocedure on the target tissue.

FIGS. 9-11 are views illustrating a nerve electrode 300, in accordancewith the principles of the present disclosure. As illustrated in theperspective view of FIG. 9, nerve electrode 300 comprises an elongatebody 302 and a cuff portion 304 extending from the elongate body 302.The elongate body 302 includes a recess 310 and a nerve contact portion320. The recess 310 is defined by finger 314 and midportion 312 ofelongate body 302 while the nerve contact portion 320 includes a firstedge 322 and a second edge 324. In one embodiment, as illustrated inFIG. 11, recess 310 includes a mouth 311 oriented in generally the samedirection as the generally curved surface of the nerve contact portion320. In another aspect, as further illustrated in FIG. 11, the recess310 defines a slot 311 that extends generally parallel to a longitudinalaxis of the elongate body 302 and in a direction proximally relative tothe nerve contact portion 320.

As further shown in the partial sectional view of FIG. 11, lead 360extends through the elongate body 302 and includes a contact electrode362 exposed at a surface of the nerve contact portion 320 of theelongate body 302. In one embodiment, the lead 360 and electrode contact362 comprises at least substantially the same features and attributes asthe lead 182 and electrode contact 180, respectively, previouslydescribed in association with FIGS. 2-7.

In general terms, the nerve contact portion 320 forms a generallyarcuate shape adapted to wrap around a portion of an outer circumferenceof the target nerve. In some embodiments, the nerve contact portion 320forms a generally semi-circular shape. In other embodiments, the nervecontact portion 320 forms a generally elliptical shape.

In another aspect, the cuff portion 304 includes a proximal portion 340and a distal portion 342. The proximal portion 340 extends directly froma first edge 322 (i.e., closed edge) of the nerve contact portion 320and is bendable relative to the first edge 322 at a point represented bydashed line A in FIG. 11. In one aspect, the cuff portion 304 is formedof a generally flexible and resilient material, so that cuff portion 304tends to maintain its shape while being adapted to flexibly movebetween: (1) a generally neutral configuration (FIGS. 9 and 11); (2) anopen, insertion configuration (indicated by dashed lines 350 in FIG.11); (3) and a releasably closed configuration (FIG. 10).

In the neutral configuration shown in FIGS. 9 and 11, distal portion 342of cuff portion 304 extends freely, independent of the elongate body302. In this neutral configuration, a surgeon can maneuver the nerveelectrode 300 adjacent to a nerve and manipulate the nerve electrode 300into a removably secured position about the nerve. In particular, thesurgeon further manipulates the cuff portion 304 into the open insertionconfiguration (represented by dashed lines 350 in FIG. 11) and thenslidably advances the distal portion 342 of cuff portion 304 underneaththe nerve. Upon pulling the distal portion 342 around the nerve, thisaction brings the nerve contact portion 320 of elongate body 302 intopressing contact against the nerve. Next, using a forceps or other tool,the surgeon removably inserts the distal portion 342 of the cuff portion304 into recess 310 of elongate body 302 to form the releasably closedconfiguration of FIG. 10. In the releasably closed configuration, thedistal portion 342 of the cuff portion 304 is removably inserted intorecess 310, thereby closing proximal portion 340 relative to nervecontact portion 320. This arrangement, in turn, encloses the cuffportion 304 about a nerve to force electrode contact 362 into contactagainst an outer surface of the nerve. The substantially larger surfacearea contact portion 320 surrounding electrode contact 362 acts a sealto prevent intrusions of fluids or other matter from interference withthe nerve to electrode interface, resulting in their stimulation signalsand or recording signals.

With cuff electrode 300 removably secured about the nerve, a surgeon canmaintain the integrity of that nerve in accordance with performingmethod 275 (FIG. 8), in accordance with use of the system 10 and nerveelectrode 150 (FIGS. 1-7), or in accordance with other methods orsystems adapted to monitor the integrity of a nerve.

FIGS. 12-14 are views schematically illustrating a nerve electrode 400,in accordance with the principles of the present disclosure. Asillustrated in the perspective view of FIG. 12 and the sectional view ofFIG. 13, nerve electrode 400 includes a proximal end 402, a distal end403, a proximal elongate body 415 that forms a trunk, and a distalnerve-engaging portion 417. For illustrative clarity, the transitionbetween the lead body 415 and the distal nerve-engage portion 417 isrepresented by dashed lines A-A, as shown in FIG. 13.

In general terms, at least a portion of the distal nerve-engagingportion 417 is configured to releasably engage a target nerve toestablish electrical communication between an electrode 440 of lead 430and an outer surface of the respective target nerve. In one embodiment,the target nerve comprises a vagus nerve within a carotid sheath, aswill be further described later in association with FIG. 14. In otherembodiments, the target nerve comprises a different nerve not locatedwithin the carotid sheath.

In one embodiment, the distal nerve-engaging portion 417 forms agenerally Y-shaped member as best seen in FIGS. 12-13. In one aspect,the Y-shaped member defines a pair of wedge-shaped fingers or branches416, 418 that are spaced apart from each other and that form an angle(τ) relative to each other. In one aspect, this arrangement provides arecess portion 420 between the respective fingers 416, 418 wherein therecess portion 420 is configured to slidably engage an outer surface ofthe target nerve, which in turn, brings an electrode contact 440 intosecure engagement in electrical conduction with the outer surface of thetarget nerve. In one embodiment, recess portion 420 comprises an atleast partially concave shape. In one embodiment, this angle (τ) betweenthe fingers 416, 418 is between about 60 and about 120 degrees, while inother embodiments, the angle (τ) is between about 80 and 100 degrees,and in still other embodiments, the angle (τ) is between about 85 and105 degrees, such as 90 degrees.

In one aspect, electrode 400 further includes electrical lead 430 thatextends proximally from the proximal end 402 of elongate body 415. Asbest seen in FIG. 13, electrical lead 430 also includes a distal portion460 that extends through a lumen 462 of, and along the length of, theelongate body 415 and the nerve-engaging portion 417. At its distal end,distal portion 460 of electrical lead 430 terminates as the electrodecontact 440 exposed at a surface of recess portion 420. In oneembodiment, the lead 430 and electrode contact 440 comprises at leastsubstantially the same features and attributes as the lead 182, 360 andelectrode contact 180, 362, respectively, as previously described inassociation with FIGS. 2-7 and 9-11.

In another aspect, as best seen in FIG. 13, each wedge-shaped finger416, 418 includes an outer side 421 and an inner side 427. In oneembodiment, the outer side 421 includes a first portion 426 and a secondportion 428 are slightly angled relative to each other and that mergetogether at peak 423. In some other embodiments, outer side 421 definesa substantially straight portion and that omits peak 423 between firstportion 426 and second portion 428.

In some embodiments, the inner side 427 and the second portion 428 ofthe outer side 421 (of each finger 416, 418) form an angle (β) of about30 degrees, and at least falls within a range of about 15 to about 45degrees. This angle (β) is selected to achieve the desired amount ofanchoring and/or amount of separation between a target nerve andadjacent structures (e.g. nerve, vein, artery, etc.) surrounding thetarget nerve.

In other embodiments, each finger 416, 418 is configured with arelatively larger angle (β) that is used to increase the amount ofseparation between the target nerve and adjacent structures, to increasethe degree of anchoring between target nerve and adjacent structure, orto occupy more space created by a relatively smaller sized target nerveor adjacent structure. In one aspect, these larger angles fall within arange between about 25 to 45 degrees. On the other hand, in someembodiments, each finger 416, 418 configured with a relatively smallerangle that is used to decrease the amount of separation between targetnerve and adjacent structures, to decrease the degree of anchoringbetween target nerve and adjacent structures, or to occupy less spacecreated by a relatively larger sized target nerve or adjacent structure.In one aspect, these smaller angles fall within a range between aboutfive and 15 degrees.

In another aspect, the generally Y-shaped member generally correspondsto the general shape of a concave quadrilateral (or concave polygon) inwhich recess portion 420 of electrode 400 is generally analogous to aconcave portion of the concave quadrilateral. In addition, a proximalregion 433 of nerve-engaging portion 417 is generally analogous to aconvex portion of a concave quadrilateral that is directly opposite theconcave portion of the concave quadrilateral. In this arrangement, thetwo sides of the concave quadrilateral that generally correspond to theinner side 427 of each finger 416,418 together form the recess portion420 of electrode 400. Meanwhile, each of the other two sides of theconcave quadrilateral generally corresponds to the respective outer side421 of the respective fingers 416, 418 and are arranged to contact asurrounding tissue on opposite sides of the distal-engaging portion 417.With this arrangement, the general concave quadrilateral shape of thenerve-engaging portion 417 effectively trisects the target nerve and twoother adjacent structures. In one aspect, this trisection of the targetnerve and surrounding tissues ensures stable and robust anchoring of thenerve-engaging portion 417 relative to the target nerve withoutencircling the target nerve, thus easing selective release the electrode400 relative to the target nerve when it is desired to remove theelectrode 400 from the target nerve. In one embodiment, both fingers416, 418 have substantially the same shape and size, while in otherembodiments, one of the respective fingers 416, 418 has a size and/orshape that is substantially different (e.g., longer, shorter, wider,narrower, etc.) than the size and/or shape of the other respectivefinger 416, 418. However, it is understood that in either case, thecombination of fingers 416, 418 provide the recess portion 420configured to engage target nerve 510. In one aspect, the embodiment ofdifferently shaped or sized fingers 416,418 is configured to accentuateseparation of target nerve 510 from the other structures within thecarotid sheath depending upon the relative size of those otherstructures and/or the relative spacing between those respectivestructures and the target nerve 510.

As further illustrated in FIG. 12, elongate body 415 also includes apair of apertures 442 adjacent proximal end 402 and a second pair ofapertures 444 located distal to the first pair of apertures 442. Therespective apertures 442 and 444 or sized and positioned on the elongatebody 415 and spaced apart from the nerve-engaging portion 417 tofacilitate suturing or otherwise fixing elongate body 415 relative tostructures surrounding or adjacent to the target nerve.

With this arrangement in mind, FIG. 14 schematically illustrates amethod 500 of releasably engaging electrode 400 against a target nerve510 (e.g., vagus nerve) within a sheath 502 (such as the carotid sheath)and relative to surrounding tissues 512, 514 (such as the internaljugular vein and the common carotid artery). After making an incision insheath 502, nerve-engaging portion 417 is introduced and advanced withinan interior space contained via sheath 502 until the recess portion 420releasably engages target nerve 510 and until the fingers 416, 418separate target nerve 510 from each of a first surrounding tissue 512(e.g., a common carotid artery) and a second surrounding tissue 514(e.g., an internal jugular vein).

Once the nerve electrode 400 is maneuvered into the position shown inFIG. 14, sutures or other biologically compatible fasteners are used toanchor elongate body 415 of electrode 400. In particular, the first pairof apertures 442 is generally located external to sheath 502 and providesites for securing sutures or other fasteners onto elongate body 415.These respective sutures or fasteners are then secured to the sheath 502or other structures. In another aspect, the second pair of apertures 444is used in a similar fashion to secure the elongate body 415 relative tothe sheath 502 and/or other surrounding structures. Accordingly,electrode 400 is robustly, releasably secured for stimulating ormonitoring nerve 510 via: (1) the general pressure of tissues withinsheath 502 that acts to maintain the nerve-engaging portion 417 in itstrisecting position between the target nerve 510 and other tissues 512,514; and (2) the suturing of elongate body 415 relative to sheath 502(or other structures) that acts to maintain an orientation of elongatebody 415 that further maintains the trisecting position of thenerve-engaging portion 417. Moreover, as seen from FIG. 14, in oneembodiment, elongate body 415 has a length configured to ensure that aproximal end 402 (and at least the first pair of apertures 442) extendexternally outside of sheath 502 when the nerve-engaging portion 417 isreleasably engaging the target nerve 510.

Embodiments of the present disclosure enable consistent and accuratemonitoring of the integrity or health of a nerve adjacent to a targettissue during a surgical procedure on that target tissue.

Although the present disclosure has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges can be made in form and detail without departing from the spiritand scope of the present disclosure.

1. An electrode assembly comprising: a nerve-engaging portion including:a pair of generally arcuate fingers; and a base hinge portion from whichthe respective fingers extend and configured to cause movement of thefingers between a closed position in which the fingers are releasably,slidably engaged in a side-by-side relationship to define a lumen and anopen position in which distal ends of the fingers are spaced apart toprovide access to the lumen, wherein the base hinge portion supports anelectrode contact exposed at a surface of the lumen; an actuatormechanism including a pair of grip members, both extending outwardlyfrom the base hinge portion and spaced apart from each other such that areleasable pressing action of the grip members relative to each othercauses movement of the fingers from the closed position to the openposition; and an electrical lead extending through one of the respectivegrip members to be in electrical communication with the electrodecontact.
 2. The electrode assembly of claim 1 wherein the pair of gripmembers includes a first grip member and a second grip member, the firstgrip member defining an elongate beam that is substantially longer thanthe second grip member, and wherein the base hinge portion includes acentral bending region that is offset relative to a longitudinal axis ofthe elongate beam.
 3. The electrode assembly of claim 2 wherein theelectrical lead extends through the elongate beam.
 4. The electrodeassembly of claim 3 wherein the electrode contact is sized and shaped tobe in alignment with the longitudinal axis of the elongate beam.
 5. Theelectrode assembly of claim 4 wherein the elongate beam and theelectrical lead extend in a substantially single direction throughout alength of the beam.
 6. The electrode assembly of claim 2 wherein theelongate beam has a length substantially greater than a diameter of thelumen of the nerve-engaging portion.
 7. The electrode assembly of claim6 wherein the elongate beam has a width substantially greater than aside edge of the elongate body.
 8. The electrode assembly of claim 1wherein the respective grip members are spaced apart at an angle between30 to 110 degrees.
 9. The electrode assembly of claim 8 wherein therespective grip members are spaced apart at an angle between 40 to 90degrees.
 10. The electrode assembly of claim 1, wherein with the fingersarranged in their side-by-side relationship, each finger is configuredwith a radial length sufficient to cause the distal end of each fingerto releasably contact a portion of the base hinge portion when thefingers are in the closed position.
 11. The electrode assembly of claim1, wherein in combination with the base hinge portion, a width of eachfinger independently defines a portion of a length of the lumen.
 12. Theelectrode assembly of claim 1 wherein the respective fingers eachinclude an angled inner edge that forms a generally helical pattern. 13.The electrode assembly of claim 12 wherein each respective fingerincludes a straight outer edge such that the angled inner edge and thestraight edge of each respective finger converges to form a curved tipat the distal end of each respective finger.
 14. The electrode assemblyof claim 1 and further comprising a system including the cuff electrodeand a monitor that comprises: a stimulation module configured toautomatically apply a stimulation signal, via the cuff electrode, to thenerve at periodic intervals; a response module configured toautomatically measure a neurogenic response signal directly from thenerve or indirectly though innervated muscle via the response electrode,wherein the response module includes an identification functionconfigured to identify potential impairment of the nerve by comparingthe measured response signals to a baseline response pattern; and a userinterface including a notify function configured to provide automaticnotification to the user of the identified potential impairment of thenerve via at least one of a visual or an audible alarm.
 15. Theelectrode assembly of claim 14 wherein the stimulation module isconfigured to enable user adjustment, via the user interface or via aremote control, a length of the periodic intervals of the stimulationsignal to apply one or more different stimulation rates.
 16. A nerveelectrode assembly comprising: an electrical lead; an elongate bodyhousing the electrical lead with the electrical lead extending at leastproximally from a proximal end of the elongate body, the elongate bodyincluding: a recess defined in a first side of the elongate body andincluding a mouth facing away from the promixal end of the elongatebody; and a distal contact portion including an electrode contact incommunication with the electrical lead, wherein the distal contactportion is located distally relative to the mouth of the recess andforms a generally arcuate shape; and a resilient arm including a distalportion and a generally semicircular proximal portion extending from thedistal contact portion of the elongate body, the arm having a lengthsufficient to cause the distal portion to extend proximally beyond thedistal contact portion of the elongate body and into the recess uponremovable, slidable insertion of the distal portion of the arm into therecess, wherein a combination of the proximal portion of the arm and thedistal contact portion of the elongate body define a lumen.
 17. Thenerve electrode claim 16 wherein the recess extends generally parallelto the first side of the elongate body, wherein the mouth of the recessis oriented in substantially the same direction as a generally concavesurface of the distal contact portion of the elongate body, and whereinthe recess defines a slot extending proximally from the mouth toward theproximal end of the elongate body.
 18. The nerve electrode of claim 16wherein elongate body includes a second side generally opposite thefirst side with the first side and the second side defining a generalwedge shape having a narrow portion adjacent the proximal end of theelongate body and a wider portion adjacent the distal contact portion ofthe elongate body.
 19. The nerve electrode of claim 16 wherein thedistal portion of the arm has a length at least two times longer than anarc length of the proximal portion of the arm.
 20. An electrode assemblycomprising: an electrical lead; and a generally Y-shaped body includingan elongate stem and a distal nerve-engaging portion, wherein the stemhouses the electrical lead and includes a proximal end from which theelectrical lead proximally extends, and wherein the distalnerve-engaging portion includes: a pair of spaced apart, generallywedge-shaped fingers extending distally from the stem and defining arecessed base portion between the respective fingers; and an electrodecontact positioned at the recessed base portion and in electricalcommunication with the electrical lead.
 21. The electrode assembly ofclaim 20 wherein each respective wedge-shaped finger defines a tipcorresponding to a narrow portion of the wedge shape and includes agenerally non-uniform thickness that increases from the tip toward thestem.
 22. The assembly of claim 20, wherein an angle of about 60 degreesto about 120 degrees is formed between a longitudinal axis of each ofthe respective fingers.
 23. The electrode assembly of claim 20 whereineach respective finger forms an inner side and an outer side, and theouter sides of the pair of fingers form a reflex angle relative to eachother, the inner sides of the pair of finger form at least one of agenerally obtuse angle or an acute angle relative to each other suchthat the generally Y-shaped body has a shape generally corresponding toa concave quadrilateral.
 24. A method of monitoring a nerve, the methodcomprising: introducing a nerve electrode through a wall of a sheath andadvancing the electrode through an interior of the sheath; maneuveringthe nerve electrode within the sheath to a cause a recess-shaped contactportion of the nerve electrode to releasably engage a target nervelocated within the sheath and to releasably anchor the nerve electroderelative to the target nerve, wherein the maneuvering action furthercomprises: interposing a trunk of the nerve electrode between a firststructure and a second structure within the sheath; interposing a firstportion of the contact portion between the target nerve and the firststructure within the sheath; and interposing a second portion of thecontact portion between the target nerve and the second structure withinthe sheath; and applying a stimulation signal to the target nerve via anelectrical lead that extends through a trunk of the nerve electrode andthat is in electrical communication with an electrode contact of recesscontact portion.
 25. The method of claim 24, comprising: furtheranchoring engagement of the contact portion relative to the target nervevia fastening the trunk of the nerve electrode relative to the sheath.26. The method of claim 25, comprising: arranging the nerve electrode asa Y-shaped member via: providing the trunk as an elongate element; andproviding a first finger and a second finger extending from the trunk toform the recess-shaped contact portion, wherein the first finger formsthe first portion of the contact portion and the second finger forms thesecond portion of the contact portion.